Heterogeneous Formation of Oriented Silicon Oxynitride on α-Si3N4 Seed Crystals : Habits And Radiation Stability

1999 ◽  
Vol 5 (S2) ◽  
pp. 778-779
Author(s):  
R.W Carpenter ◽  
W Braue ◽  
M.J. Kim
Keyword(s):  
Silicon Nitride ◽  
Heterogeneous Nucleation ◽  
Radiation Stability ◽  
Silicon Oxynitride ◽  
Minor Constituent ◽  
Sintering Aids ◽  
Sintering Aid ◽  
Nucleation Sites ◽  
Heterogeneous Formation ◽  
A Minor

Lath-like silicon oxynitride crystals have often been observed in the microstructure of silicon nitride based ceramics after processing. They are usually located in glassy regions which are siliceous solidified sintering aid liquid, and usually contain a small (∼100nm) a-Si3N4 crystal. These nitride crystals are considered to be seeds, incompletely dissolved in the melt, that are heterogeneous nucleation sites for the oxynitride crystals. We present here the first observations of morphological and crystallographic habits between the seed nanocrystals and the host oxynitride laths.Fig. 1 shows a typical oxynitride lath containing a nitride seed crystal. The lath is surrounded by glass and ß-Si3N4 particles, and a small cristobalite particle (a minor constituent). This microstructure is from an Si02-Si3N4 ceramic processed with Al2O3 sintering aid. The same oxynitride lath/seed structures were observed when other sintering aids (eg. Y2O3, MgO, ZrO2) were used, so they are independent of sintering aid.

Effects of Sintering Conditions and Additives on Translucent Silicon Nitride Ceramics

2012 ◽  
Vol 724 ◽  
pp. 282-286 ◽  
Author(s):  
Wen Wu Yang ◽  
Miki Inada ◽  
Yumi Tanaka ◽  
Naoya Enomoto ◽  
Junichi Hojo
Keyword(s):  
Silicon Nitride ◽  
Visible Region ◽  
Sintering Aids ◽  
Sintering Aid ◽  
Sintering Additives ◽  
Nitride Ceramics ◽  
Sintering Conditions

Translucent β-Si3N4 sintered ceramics have been fabricated by using AlN-MgO sintering additives. In the present study, the authors employed AlN-MgO as a standard sintering aid, and investigated the effects of sintering conditions on the translucency of Si3N4. Furthermore, various oxides such as HfO2, Sm2O3, Y2O3, Sc2O3, La2O3, Nd2O3, CeO2, CaO, ZrO2 etc. were used as the sintering aids of Si3N4, and the sintered β-Si3N4 ceramics exhibited different transmittances in the visible region. It was found that the transmittance of sintered ceramics was mainly affected by the sintering additives.

Crystallization of Zirconium Nitride in Silicon Nitride Ceramics with Nitrogen Pressures and Sintering Additives

2005 ◽  
Vol 287 ◽  
pp. 253-258 ◽  
Author(s):  
S.M. Lee ◽  
K.H. Park ◽  
Jung Whan Yoo ◽  
Hyung Tae Kim
Keyword(s):  
Mechanical Properties ◽  
Silicon Nitride ◽  
Surface Region ◽  
Nitrogen Atmosphere ◽  
Zirconium Nitride ◽  
Sintering Aids ◽  
Sintering Aid ◽  
Heat Treated ◽  
Nitride Ceramics ◽  
Sintered Silicon

We investigated grain boundary crystallization of gas-pressure-sintered silicon nitride with zirconia and magnesia as sintering aids. Cation compositions were mostly uniform throughout the specimen however, ZrO2 was crystallized in the surface region, while ZrN in the inside. When the specimen was heat-treated at 1 atm nitrogen atmosphere, ZrO2 in the surface region transformed to ZrN. The transformation, however, was suppressed when alumina was incorporated as an additional sintering aid. Based on these results, we propose a model describing the reaction among Si3N4, SiO2, ZrO2, ZrN and N2. Observed microstructures and measured mechanical properties were consistent with the model.

Influence of Sintering Aids on the Sintering and Conductivity Properties of Si3N4 Composites

2016 ◽  
Vol 697 ◽  
pp. 457-461
Author(s):  
Yong Jiang ◽  
Lan Er Wu ◽  
Wan Xiu Hai
Keyword(s):  
Diffusion Coefficient ◽  
Rare Earth ◽  
High Temperature ◽  
Silicon Nitride ◽  
Light Rare Earth ◽  
Sintering Aids ◽  
Si3n4 Ceramic ◽  
Sintering Aid ◽  
Self Diffusion ◽  
Self Diffusion Coefficient

Silicon nitride (Si3N4) is one of the most important engineering materials. The developing trend of Si3N4 ceramic should be its composite with reinforce phase. However, due to its low self-diffusion coefficient at high temperature, the Si3N4 is very hard to be densified without sintering aids. In the present work, the Y2O3 and light rare-earth oxides of La series (La2O3, CeO2, Pr2O3, Sm2O3) and AlN, Al2O3, MgO, CaCO3 were chosen to be sintering aids. Their effect on the sintering of Si3N4 composite was studied. The results showed that the Y2O3 was the best sintering aid in all members, and the Y2O3-La2O3-AlN ternary composition was the best formula.

Transient Viscous Phase Reaction Sintered (Tvprs) Silicon Oxynitride Ceramics.

1992 ◽  
Vol 287 ◽  
Author(s):  
Kevin P. Plucknett ◽  
David S. Wilkinson
Keyword(s):  
Weight Loss ◽  
Silicon Nitride ◽  
Nitrogen Atmosphere ◽  
Silicon Oxynitride ◽  
Phase Reaction ◽  
Reaction Sintering ◽  
Sintering Aids ◽  
Powder Bed ◽  
Sintering Conditions ◽  
Composite Silicon

High density silicon oxynitride ceramics were fabricated by reaction-sintering a mixtureof silicon nitride and silica without the use of sintering aids. Precursor silicon nitride compacts were prepared by conventional means after which they were subjected to a lowtemperature oxidation heattreatment (∼1000ºC) producing a composite silicon nitride/silica compact. Oxidized compacts were then reaction-sintered in a nitrogen atmosphere at temperatures between 1400 and 1800ºC using a range of protective ‘powder-bed’ compositions. A ‘powder-bed’ comprising a mixture of boron nitride, silicon nitride and silica was found to be most effective in preventing decomposition and subsequent weight loss. Nearly complete reactive transformation to silicon oxynitride was observed under optimised sintering conditions.

Tensile Creep of Y-Si3N4: II. Cavitation

1991 ◽  
Vol 49 ◽  
pp. 972-973 ◽  
Author(s):  
B. J. Hockey ◽  
S. M. Wiederhorn
Keyword(s):  
Silicon Nitride ◽  
Creep Rupture ◽  
Tensile Creep ◽  
Sintering Aids ◽  
Microstructural Changes

ATEM has been used to characterize three different silicon nitride materials after tensile creep in air at 1200 to 1400° C. In Part I, the microstructures and microstructural changes that occur during testing were described, and consistent with that description the designations and sintering aids for these materials were: W/YAS, a SiC whisker reinforced Si3N4 processed with yttria (6w/o) and alumina (1.5w/o); YAS, Si3N4 processed with yttria (6 w/o) and alumina (1.5w/o); and YS, Si3N4 processed with yttria (4.0 w/o). This paper, Part II, addresses the interfacial cavitation processes that occur in these materials and which are ultimately responsible for creep rupture.

Characterization of Hot-Pressed Silicon Nitride Ceramics with Alkoxide-Derived Oxide Mixtures As the Sintering Aid

1992 ◽  
Vol 287 ◽  
Author(s):  
Y. Sato ◽  
C. Sakurai ◽  
M. Ueki ◽  
K. Sugita
Keyword(s):  
Mechanical Properties ◽  
Room Temperature ◽  
Weight Ratio ◽  
Sintering Aids ◽  
Sintering Aid ◽  
Oxide Powders ◽  
Nitride Ceramics ◽  
Final Weight ◽  
Alkoxide Method

ABSTRACTA homogeneous mixture of Y2O3, CeO2 and MgO with a final weight ratio of 3:1: 2 was prepared by the alkoxide method. The powder mixture was then added into Si3N4 powder in amounts ranging from 4 to 12 wt%, andconsolidated by hot-pressing. Microstructure and mechanical properties of the sintered bodies were determined and compared to those of materials prepared by the conventional route of mixing the oxide powders as sintering aids individually in essentially same composition. The β-fraction (modification ratio) in same composition was higher in thesintered bodies made through the alkoxide method than those made through the conventional one. The room temperature flexural strength was maximized with 6wt% addition of the alkoxide derived oxide, whereas, 12wt% addition of the total oxide was required to maximize the strength by conventional processing.

scholarly journals Influence of ZnO addition and milling process on structure and conductivity of BaCe0.2Zr0.7Y0.1O3-δ ceramics

2021 ◽  
Vol 15 (3) ◽  
pp. 288-296
Author(s):  
Ana Ana Kaori de Oliveira Ouba ◽  
Adilson Chinelatto ◽  
Edson Grzebielucka ◽  
Kethlinn Ramos ◽  
Janaina Borcezi ◽  
...  
Keyword(s):  
Secondary Phase ◽  
Linear Shrinkage ◽  
High Energy ◽  
Milling Process ◽  
Sintering Aids ◽  
X Ray Diffraction ◽  
Sintering Aid ◽  
Secondary Phase Formation ◽  
Precursor Powders ◽  
Perovskite Lattice

Precursor powders for BaCe0.2Zr0.7Y0.1O3-?(BCZY27) ceramics were synthesized by a modified Pechinimethod and calcined at 900?C for 12 h. The calcined BCZY27 powders were milled in eccentric and in high energy mill with the addition of 2 and 4mol% ZnO as sintering aid. The effects of milling and sintering aids on the sinterability and electrical conductivity were studied. The linear shrinkage in thermomechanical analyses started at 1050?C for the BCZY27 with 4mol% ZnO processed in eccentric mill. Theoretical density above of 90%TD was obtained for the BCZY27 milled with 4mol% ZnO and sintered at 1400?C for 4h. X-ray diffraction analysis of the BCZY27 ceramics sintered at 1400?C confirmed the presence of BaCe0.2Zr0.7Y0.1O3-? and Y0.4Ce0.6O1.8 phases. The incorporation of Zn into perovskite lattice leads to the secondary phase formation. SEM and EDS analyses confirmed the presence of Y0.4Ce0.6O1.8 phase. The sintering was assisted by BaO-ZnO eutectic, which was reflected by the increase of activation energy values for grain boundary conduction. The milling processing did not affect the conductivity properties. The obtained BCZY27 dense sample has conductivity of 7.60 ? 10?3 S/cm at 500?C.

Geometric Design of Heterogeneous Nucleation Sites on Biocompatible Surfaces

2013 ◽  
Vol 13 (8) ◽  
pp. 3835-3841 ◽  
Author(s):  
Vilmalí López-Mejías ◽  
Allan S. Myerson ◽  
Bernhardt L. Trout
Keyword(s):  
Heterogeneous Nucleation ◽  
Geometric Design ◽  
Nucleation Sites

scholarly journals Betaine Yields from Marine Algal Species Utilized in the Preparation of Seaweed Extracts Used in Agriculture

2010 ◽  
Vol 5 (4) ◽  
pp. 1934578X1000500 ◽  
Author(s):  
Gerald Blunden ◽  
Peter F. Morse ◽  
Imre Mathe ◽  
Judit Hohmann ◽  
Alan T. Critchley ◽  
...  
Keyword(s):  
Marine Algae ◽  
Algal Species ◽  
First Record ◽  
Commercial Production ◽  
The Other ◽  
Minor Constituent ◽  
Laminaria Digitata ◽  
Seaweed Extracts ◽  
Marine Algal ◽  
A Minor

Ascophyllum nodosum, and to a lesser extent, Laminaria digitata, L. hyperborea and Fucus serratus, are marine algal species utilized in the commercial production of seaweed extracts used in agriculture. Betaines have been shown to be important constituents of these extracts, but there appears to have been no study made on whether there are variations in the betaine contents of these species based on either the place or date of collection. Samples of each of the four species were collected from widely separated areas at different times of the year. Also, in the case of A. nodosum, approximately monthly collections were made from one location. The betaines detected in the various collections of the same species showed little variation, although in the case of A. nodosum, glycinebetaine was found as a minor constituent in some samples, but was not detected in others. Trigonelline was found in all the tested samples of the two Laminaria species; this is, to our knowledge, the first record of this betaine in marine algae. With the exception of trigonelline in the Laminaria species, the betaine yields from the various samples of L. digitata, L. hyperborea and F. serratus showed little variation, regardless of either the place or date of collection. The trigonelline contents of the Laminaria species collected at one location (Finavarra, Ireland), in particular of L. hyperborea, was substantially greater than those from the other places of collection. In the case of A. nodosum, the betaine yields from samples collected at one site (Dale, Pembrokeshire, UK) were significantly higher than those from the other places of collection, which were very similar to each other. There was no clear indication of seasonal variation in betaine yields from A. nodosum.

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